Process of treating sugar solutions with ion-exchange resins



Patented Aug. 18, 1953 PROCESS OF TREATING SUGAR SOLUTIONS WITHION-EXCHANGE RESINS James C. Winters, Glenside, Pa., and Robert Kunin,Trenton, N. J., assignors to Rohrn 8g Haas Company, Philadelphia, Pa., acorporation of Delaware No Drawing. Original application April 13, 1948,

Serial No. 20,847.

Divided and this application November 13, 1950, Serial No. 195,466

4 Claims. (01. 127-146) This invention is an improvement in thedeionization of aqueous sugar solutions by means of ion-exchangematerials. This application is a division of our copending applicationSerial No. 20,847, filed April 13, 1948, which issued May 1, 1951, as U.S. Patent No. 2,551,519.

It is known that in the processing of both sugar beet and cane sugarjuices the presence of inorganic salts in sugar solutions interfereswith the recovery of the sucrose. It is also known that the salts ofdifferent metals have different effects and that the alkaline earthmetals such as calcium are much more melassigenic than is sodium. Thepresence of calcium in refinery solutions is also objectionable for thereason that its salts are primarily responsible for the scale that formson the evaporators. To overcome these salt effects, it has heretoforebeen proposed to deionize the defecated raw sugar juice by passing itfirst through a bed of cation-exchange resin wherein hydrogen from theresin is ex-' changed for the cations of the salt in solution and thenthrough a bed of anion-exchange resin which adsorbs the acid formed inthe bed of cation-exchange material. Usually the juice is passed in thisfashion through a series of alternating cationand anion-exchange bedsand the salt content of the juice reduced in steps. A disadvantage ofthis process as it is currently practiced is that the acidic conditionof the juice leaving the cation-exchange bed is conducive to theinversion of the sucrose. To overcome this, the juice must be reduced toa temperature of approximately 20 C., a practice that is economicallyfeasible only where low temperature cooling water is available in largeamounts. A further disadvantage of the process as currently practiced isthat the high calcium content of the defecated juice requires thatspecial regenerating techniques be employed for the most economicaloperation.

The cation-exchange materials heretofore used in deionizing sugarsolutions are those that contain strongly acidic polar groups such assulfonate or sulfate. Sulfonated coals, sulfonated phenol-formaldehyderesins, and sulfonated styrene-divinyl benzene copolymers are examplesof such materials. These materials, having strongly acidic groups, havethe power to split neutral salts; i. e., to replace the cation of thesalt with hydrogen from the exchange material. To regenerate themrequires the use of fairly stron acid. Sulfuric acid is the cheapeststrong acid available and its use is desirable whenever (I thus removedis calcium.

possible. It cannot, however, be used directly to regenerate thesesulfonate exchange materials when they are loaded with calcium ion forthe reason that insoluble calcium sulfate forms on the particles ofexchanger and interferes with their operation. To overcome this, it hasbeen proposed to remove the calcium from the exchanger by ion-exchangewith asolutionoi common salt and then regenerate with sulfuric acid.

We have now found the objectionablev effects of the presence of calciumsalt in sugar solutions can be eliminated without the generatiqn of alow pH in the solution by pas i g defecated juice through a bed ofcationexchangematerial in which the polar groups are. m e ync acidgroups. The carbvoggylic cation-exchange resins in their acidic form areonly wealgly acidic and do not split salts to any substantial degree.Nevertheless we have found that from one-third to one-half the ashcontent of a sugar solution as it leaves the normal defecation step canbe removed by one passage of the solution through a bed of this typeexchanger. Most of the ash lhere is, therefore, provided a means ofsubstantially reducing the salt content of the sugar solution and ofpractically eliminating the objectional effects of calcium while at thesame time avoiding the low pH that is encountered in the deionizationprocesses heretofore proposed.

Unlike the sulfonate type exchange materials, the carboxylic type can beregenerated with very weak acids whereby the problem of calciumprecipitation is avoided. These resins may also be regenerated by meansof an aqueous solution of carbon dioxide under pressure whereby calciummay be removed as the bicarbonate.

The carboxylic acid resins that we prefer to use are thosecrossed-linked polymers of poly-.- merizable acids described in U. S.Patents Nos. 2,340,110 and 2,340,111. Particularly suitable are thecrossed-linked polymers of acrylic acid, or methacrylic acid, or maleicacid such as are obtainable by the joint polymerization of one or moreof the acids with divinyl benzene. In such resins the divinyl benzene orother cross-linking component renders the resins insoluble, and it isdesirable to use an amount not substantially higher than willaccomplishthis. From 2 /2% to 10% of divinyl benzene based on the weightof polymerizable acid is a practical operating range.

When it is not desired to effect a further reduction in ash content thanis accomplished by passing the sugar solution through a bed ofcarboxylic cation-exchange resin, the pH of the efliuent solution may becontrolled by using the resin in a mixed acid-sodium salt form ratherthan in a fully acidic form. The efiluent from a bed of these resins intheir fully acidic form will have a pH that may be as low as, but notlower than, about 3.5. This may be a lower pH than is desired to haveexist in the evaporators. A higher pH in the efiluent solution willresult from the use of a mixed acid and sodium salt form of resin whichmay be readily prepared by treating the resin as in regeneration with asolution of sodium salt and acid. By varying the ratio of salt to acidin such a mixture, the ratio of sodium salt groups to acid groups in thetreated resin may be varied; and the greater the number of sodium saltgroups in the resin the higher will be the pH of the efliuent. In thisway the pH of the efliuent may be adjusted to neutrality if desired.

Alternatively, the sugar solution after passage through the bed ofcarboxylic type cation-exchange resin may be passed in the usual fashionthrough a bed of anion-exchanger. The anionexchanger may be of the typeheretofore used wherein the polar groups are amino groups or it may beof the new quaternary ammonium type. The amino type anion-exchangers areexemplified by the phenol formaldehyde-polyalkylene polyamine describedin U. S. Patent No. 2,402,384. These resins in their basic form willadsorb free acid from solutions but have little or no effect uponneutral salts contained in the solution. By their use the pH of thesugar solution leaving the anion resin exchanger will be raised toapproximately 9-9.5.

Deionization may be continued by passing the solution through a seriesof alternating carboxylic type cation-exchange beds and amino typeanion-exchange beds, but subsequent beds of carboxylic exchanger willnot remove as large a quantity of metallic ions from the solution asdoes the first bed. It will, therefore, require a number of alternatingbeds to complete deionization. This method of practicing our inventionhas the advantage of maintaining the pH of the sugar solution at alltimes between the limits of about 3.5 and 9.5 but the disadvantage ofrequiring a considerable series of alternating beds for completedeionization.

Complete deionization in fewer additional pairs of beds can beaccomplished either by using as the anion-exchanger a quaternaryammonium type of anion-exchange resin or by using in a second bed ofcation-exchanger a sulfonate type of cation-exchanger. The quaternaryammonium type of anion-exchanger is obtainable by haloalkylating a baseresin containing aromatic groups and then replacing the halogen by aquaternary ammonium group by reacting with a tertiary amine. In patentapplication Serial No. 759,308, new Patent Number 2,591,573, filed July5, 1947, there are disclosed resins of this class made bychloromethylating a copolymer of a monovinyl aromatic compound and adivinyl aromatic compound and reacting the chloromethylated polymer withtrimethylamine or a similar tertiary amine. A copolymer of styrene anddivinyl benzene is the base resin recommended. These quaternary ammoniumanion-exchangers, like the sulfonated cation-exchangers, have theability to split salts but in so doing they remove the anion rather thanthe cation. They will, for example, remove chloride ion from a sodiumchloride solution. When used in the second bed of a sugar solutiondeionization process, they will remove anions to such an extent that thepH of the solution passing through the bed reaches as high as 12.Additional cations may then be removed by passing the solution through asecond bed of carboxylic exchanger, and by repeating the alternatingbeds the solution may be rapidly deionized. The deionization of sugarsolutions by passing them through alternating beds of first a quaternaryammonium exchanger and then a carboxylic resin is described and claimedin copending application Serial No. 20,836 of Charles H. McBurney filedApril 13, 1948.

Instead of using the carboxylic type resin for the second and subsequentcation-exchange beds, a sulfonated cation-exchanger may be used at thesestages without all of the disadvantages heretofore mentioned incident tothe use of this type of exchanger. Some acidity in the efiiuent mayresult from its use, particularly if an anionexchanger having aminopolar groups is used; but this acidity will be less serious than What iscurrently met and, if necessary, can be overcome by the same techniques.

When an initial bed of carboxylic acid cationexchange resin is used inconjunction with subsequent beds of sulfonate type of cation-exchangeresin, it is not necessary that a bed of anionexchange resin beinterposed between the bed of carboxylic acid resin and the first bed ofsulfonate type resin. Instead, the sugar solution may be passed directlyfrom the carboxylic resin bed to the sulfonated resin bed. In this modeof operating, the carboxylic acid resin functions to remove the metalsthat are present as their hydroxide or as salts of very weak acidsleaving the full capacity of the sulfonated resins to operate upon thesalts of stronger acids. This will result in acidity being formed in thesugar solution, but it has the marked advantage of permitting the use ofa smaller bed of sulfonate exchanger or the sugar solution can be morerapidly passed to the anion-exchanger wherein the acidity is removed. Afurther advantage of this combination over the use of a sulfonatedexchanger alone as the first bed resides in the fact that the very highcapacity of the carboxylic exchangers and the utilization of the lowercapacity sulfonated exchangers only to split the salts of stronger acidspermit less frequent regeneration of the beds.

This invention is particularly applicable to the treatment of thedefecated raw sugar juices; that is, the clarified raw juice after ithas been limed with or without carbonation, sulfitation, or treatmentwith phosphoric acid, and to the treatment of the afiination syrup whichis obtained from the washing of a raw cane sugar cake particularly whenthe aiiination syrup is limed and defecated. It may, however, also beapplied to the sweet water obtained from the washing of materials orequipment such as the filter washings and to the char wash liquorsobtained in washing the sugar from exhausted bone char. Thus, theprocess of this invention can be used in the de-ashing of sugarsolutions which are as dilute as sweet water or as concentrated assyrups.

The following examples are given to illustrate the extent of ash removalthat may be accomplished by passing sugar syrup through a bed ofcarboxylic acid type cation-exchange resin.

Example 1 Sugar beet solution, after the carbonation step and having aconcentration of 12 Brix, a pH of 9.42, and an ash content of 0.22%, waspassed through a column of cation-exchange resin that was a copolymer of95 parts of methacrylic acid and 5 parts of divinyl benzene. Samples ofefliuent leaving the column were withdrawn from time to time andanalyzed. After four volumes of solution per volume of resin had passedthrough the column, the sample withdrawn had a pH of approximately 4 andan ash content of approximately 0.09%. When eight volumes of solutionper volume of resin had passed through, a sample withdrawn had a pH ofapproximately 4.4 and an ash content of 0.10%. After sixteen volumes hadpassed, the efiluent had a pH of approximately 4.7 and an ash content ofapproximately 0.12%, At the thirty-two volume mark, the sample ofeflluent had a pH of approximately 5 and an ash content of approximately0.13%. The pH and ash content of the effluent continued to risegradually. The passage of solution through the column may bediscontinued at any desired point.

Example 2 A defecated can sugar solution, having a pH of 6.2 and an ashcontent of 0.147%, was passed through a column of resin as in Example 1.After twelve volumes of solution per volume of resin had passed throughthe column, a sample of efiluent as it left the column had a pH of 4.2and an ash content of 0.106%. As in Example 1, the pH and ash content ofthe effluent thereafter continued to rise gradually and the operationmay be discontinued at any desired point.

The carboxylic resins used in these examples may be regenerated bypassing through the column a slight excess over the stoichiometricequivalent of strong mineral acid in concentration as low as 0.01 molar.At this concentration of sulfuric acid insoluble calcium sulfate is notformed and the use of this acid is, therefore, permitted.

After the reduction in ash content, as illustrated in these examples, asugar solution may, if desired, be treated to remove the remaining ashby any of the procedures above-mentioned. As the final step of adeionization process, the pH of the deionized solution may be adjustedby passing the deionized solution through a bed of carboxylic resin thatis in a mixed sodium and hydrogen form and in which the ratio of sodiumto replaceable hydrogen is so adjusted as heretofore described so thatthe effluent will have the pH desired. Such a bed of resin acts on thedeionized solution as a buffer and may be used for long periods withoutneed for a readjustment of the ratio of sodium salt groups to acidgroups in it.

We claim:

1. The method of purifying a dilute sucrose solution containingdissolved salts which comprises the three essential steps of directingthe solution first through a bed of cation-exchange resin in which theprincipal polar groups are carboxylic acid groups, next through a bed ofanion-exchange resin in which the principal polar groups are quaternaryammonium hydroxyl groups, and then through a bed of cation-exchangeresin in which the principal polar groups are carboxylic acid groups.

2. The method of purifying a dilute sucrose solution containingdissolved salts which comprises the three essential steps of directingthe solution first through a bed of cation-exchange resin which is across-linked polymer of a polymerizable carboxylic acid, next through abed of anion-exchange resin containing quaternary ammonium hydroxylgroups attached through methylene groups to aromatic rings in the resin,and then through a bed of cation-exchange resin which is a cross-linkedpolymer of a polymerizable carboxylic acid.

3. The method of purifying a dilute sucrose solution containingdissolved salts which comprises the three essential steps of directingthe solution first through a bed of cation-exchange resin which is acopolymer of divinyl benzene and a member of the class consisting ofacrylic, methacrylic, and maleic acids, next through a bed ofanion-exchange resin containing quaternary ammonium hydroxyl groupsattached by methylene groups to the aromatic nuclei of a cross-linkedstyrene polymer, and then through a bed of cation-exchange resin whichis a copolymer of divinyl benzene and a member of the class consistingof acrylic, methacrylic, and maleic acids.

4. The method of purifying a dilute sucrose solution containingdissolved salts which comprises the three essential steps of directingthe solution first through a bed of cation-exchange resin which is acopolymer 2 to 10% of divinyl benzene and to 97 /2% methacrylic acid,next through a bed of anion-exchange resin containing quaternaryammonium hydroxyl groups attached by methylene groups to the aromaticnuclei of a copolymer of styrene and divinyl benzene, and then through abed of cationexchange resin which is a copolymer 2 to 10% divinylbenzene and 90% to 97 /2 methacrylic acid.

JAMES C. WINTERS. ROBERT KUNIN.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,319,359 Wassenegger May 18, 1943 2,404,367 Durant et al July23, 1946 2,490,716 Smith Dec. 6, 1949 OTHER REFERENCES Bauman: ImprovedSynthetic Ion Exchange Resin, Ind. and Eng. Chem, January 1946, pages 460 (page 47 pertinent).

1. THE METHOD OF PURIFYING A DILUTE SUCROSE SOLUTION CONTAININGDISSOLVED SALTS WHICH COMPRISES THE THREE ESSENTIAL STEPS OF DIRECTINGTHE SOLUTION FIRST THROUGH A BED OF CATION-EXCHANGE RESIN IN WHICH THEPRINCIPAL POLAR GROUPS ARE CARBOXYLIC ACID GROUPS, NEXT THROUGH A BED OFANION-EXCHANGE RESIN IN WHICH THE PRINCIPAL POLAR GROUPS ARE QUATERNARYAMMONIUM HYDROXYL GROUPS, AND THEN THROUGH A BED OF CATION-EX CHANGERESIN IN WHICH THE PRINCIPAL POLAR GROUPS ARE CARBOXYLIC ACID GROUPS.